354 THE CELL 



entirely superfluous. Neither Niigeli nor de Vries consider that 

 the ancestral plasms have this construction ; they assume rather 

 that the units contained in the two hereditary masses are capable 

 of mixing with one another. Neither can I imagine that, during 

 the process of hereditary transmission, the idioblasts of paternal 

 and maternal origin continue as parts of two separated elemental 

 germs, it seems more likely that they unite together in some 

 way or other to form a compound elemental germ. 



How then, on this supposition, is the summation of the here- 

 ditary mass, occasioned by the act of sexual generation, to be 

 avoided ? I do not think that there is the slightest difficulty 

 if we assume the divisibility of the hereditary mass as a whole. 

 Even Weismann has assumed that this is possible at the beginning 

 of sexual generation, otherwise, a summation of the ancestral 

 plasms, could not have taken place without causing an increase of 

 the hereditary mass. 



But the hereditary mass can only be divided, without its pro- 

 perties being altered, if several individual units of each different 

 kind are present in it. Since the progeny are produced from two 

 almost equal combinations of elemental germs, derived from 

 the parents, there must be at least two individuals of every kind 

 of idioblast in the embryo. Nothing prevents us, however, from 

 conceiving that, instead of two individuals of each kind, there may 

 be four, eight, or speaking generally, a number of equivalent 

 idioblasts in the hereditary mass. Then it is self-evident, that a 

 reduction of mass, without the essential nature of the idioplasm 

 itself being altered, is possible in the same manner, as has been 

 observed during the maturation of the sexual products, and there- 

 fore any further complicated hypotheses are superfluous. 



In order to explain the so-called reversion to an ancestral type, 

 we need not assume the existence of ancestral plasms, for, as 

 will be seen later, the elemental germs may themselves remain 

 latent. 



4. Isotropy of Protoplasm. Various investigators have at- 

 tempted to ascribe to the whole egg a very complex organisa- 

 tion, namely, that it is composed of very minute particles, the 

 arrangement of which corresponds to that of the organs of 

 the mature animal. The clearest conception of this subject 

 is that formulated by His in his " Princip der organbildenden 

 Keimbezirke." According to this author, "on the one hand, 

 every point in the embryonal area of the germinal disc must cor- 



